函数原型：
public boolean onKeyDown(int keyCode, KeyEvent event);
第一个参数是用户按下键时，当前所接收到的按键代号；
第二个参数是按键事件的对象。
使用方法：
如果要使用这个方法。直接在主 acivity 中重写即可，一般使用开关语句 switch 来把keyCode 和 （event.按键类型） 对比来执行对应的操作。
下面我们来看下event 的按键属性都有哪些。
在上面的函数中，按住control 加 鼠标左键点击 KeyEvent，就可以点进去看到很多东西。
1 public class KeyEvent extends InputEvent implements Parcelable { 2 /** Key code constant: Unknown key code. */ 3 public static final int KEYCODE_UNKNOWN = 0; 4 /** Key code constant: Soft Left key. 5 * Usually situated below the display on phones and used as a multi-function 6 * feature key for selecting a software defined function shown on the bottom left 7 * of the display. */ 8 public static final int KEYCODE_SOFT_LEFT = 1; 9 /** Key code constant: Soft Right key. 10 * Usually situated below the display on phones and used as a multi-function 11 * feature key for selecting a software defined function shown on the bottom right 12 * of the display. */ 13 public static final int KEYCODE_SOFT_RIGHT = 2; 14 /** Key code constant: Home key. 15 * This key is handled by the framework and is never delivered to applications. */ 16 public static final int KEYCODE_HOME = 3; 17 /** Key code constant: Back key. */ 18 public static final int KEYCODE_BACK = 4; 19 /** Key code constant: Call key. */ 20 public static final int KEYCODE_CALL = 5; 21 /** Key code constant: End Call key. */ 22 public static final int KEYCODE_ENDCALL = 6; 23 /** Key code constant: '0' key. */ 24 public static final int KEYCODE_0 = 7; 25 /** Key code constant: '1' key. */ 26 public static final int KEYCODE_1 = 8; 27 /** Key code constant: '2' key. */ 28 public static final int KEYCODE_2 = 9; 29 /** Key code constant: '3' key. */ 30 public static final int KEYCODE_3 = 10; 31 /** Key code constant: '4' key. */ 32 public static final int KEYCODE_4 = 11; 33 /** Key code constant: '5' key. */ 34 public static final int KEYCODE_5 = 12; 35 /** Key code constant: '6' key. */ 36 public static final int KEYCODE_6 = 13; 37 /** Key code constant: '7' key. */ 38 public static final int KEYCODE_7 = 14; 39 /** Key code constant: '8' key. */ 40 public static final int KEYCODE_8 = 15; 41 /** Key code constant: '9' key. */ 42 public static final int KEYCODE_9 = 16; 43 /** Key code constant: '*' key. */ 44 public static final int KEYCODE_STAR = 17; 45 /** Key code constant: '#' key. */ 46 public static final int KEYCODE_POUND = 18; 47 /** Key code constant: Directional Pad Up key. 48 * May also be synthesized from trackball motions. */ 49 public static final int KEYCODE_DPAD_UP = 19; 50 /** Key code constant: Directional Pad Down key. 51 * May also be synthesized from trackball motions. */ 52 public static final int KEYCODE_DPAD_DOWN = 20; 53 /** Key code constant: Directional Pad Left key. 54 * May also be synthesized from trackball motions. */ 55 public static final int KEYCODE_DPAD_LEFT = 21; 56 /** Key code constant: Directional Pad Right key. 57 * May also be synthesized from trackball motions. */ 58 public static final int KEYCODE_DPAD_RIGHT = 22; 59 /** Key code constant: Directional Pad Center key. 60 * May also be synthesized from trackball motions. */ 61 public static final int KEYCODE_DPAD_CENTER = 23; 62 /** Key code constant: Volume Up key. 63 * Adjusts the speaker volume up. */ 64 public static final int KEYCODE_VOLUME_UP = 24; 65 /** Key code constant: Volume Down key. 66 * Adjusts the speaker volume down. */ 67 public static final int KEYCODE_VOLUME_DOWN = 25; 68 /** Key code constant: Power key. */ 69 public static final int KEYCODE_POWER = 26; 70 /** Key code constant: Camera key. 71 * Used to launch a camera application or take pictures. */ 72 public static final int KEYCODE_CAMERA = 27; 73 /** Key code constant: Clear key. */ 74 public static final int KEYCODE_CLEAR = 28; 75 /** Key code constant: 'A' key. */ 76 public static final int KEYCODE_A = 29; 77 /** Key code constant: 'B' key. */ 78 public static final int KEYCODE_B = 30; 79 /** Key code constant: 'C' key. */ 80 public static final int KEYCODE_C = 31; 81 /** Key code constant: 'D' key. */ 82 public static final int KEYCODE_D = 32; 83 /** Key code constant: 'E' key. */ 84 public static final int KEYCODE_E = 33; 85 /** Key code constant: 'F' key. */ 86 public static final int KEYCODE_F = 34; 87 /** Key code constant: 'G' key. */ 88 public static final int KEYCODE_G = 35; 89 /** Key code constant: 'H' key. */ 90 public static final int KEYCODE_H = 36; 91 /** Key code constant: 'I' key. */ 92 public static final int KEYCODE_I = 37; 93 /** Key code constant: 'J' key. */ 94 public static final int KEYCODE_J = 38; 95 /** Key code constant: 'K' key. */ 96 public static final int KEYCODE_K = 39; 97 /** Key code constant: 'L' key. */ 98 public static final int KEYCODE_L = 40; 99 /** Key code constant: 'M' key. */ 100 public static final int KEYCODE_M = 41; 101 /** Key code constant: 'N' key. */ 102 public static final int KEYCODE_N = 42; 103 /** Key code constant: 'O' key. */ 104 public static final int KEYCODE_O = 43; 105 /** Key code constant: 'P' key. */ 106 public static final int KEYCODE_P = 44; 107 /** Key code constant: 'Q' key. */ 108 public static final int KEYCODE_Q = 45; 109 /** Key code constant: 'R' key. */ 110 public static final int KEYCODE_R = 46; 111 /** Key code constant: 'S' key. */ 112 public static final int KEYCODE_S = 47; 113 /** Key code constant: 'T' key. */ 114 public static final int KEYCODE_T = 48; 115 /** Key code constant: 'U' key. */ 116 public static final int KEYCODE_U = 49; 117 /** Key code constant: 'V' key. */ 118 public static final int KEYCODE_V = 50; 119 /** Key code constant: 'W' key. */ 120 public static final int KEYCODE_W = 51; 121 /** Key code constant: 'X' key. */ 122 public static final int KEYCODE_X = 52; 123 /** Key code constant: 'Y' key. */ 124 public static final int KEYCODE_Y = 53; 125 /** Key code constant: 'Z' key. */ 126 public static final int KEYCODE_Z = 54; 127 /** Key code constant: ',' key. */ 128 public static final int KEYCODE_COMMA = 55; 129 /** Key code constant: '.' key. */ 130 public static final int KEYCODE_PERIOD = 56; 131 /** Key code constant: Left Alt modifier key. */ 132 public static final int KEYCODE_ALT_LEFT = 57; 133 /** Key code constant: Right Alt modifier key. */ 134 public static final int KEYCODE_ALT_RIGHT = 58; 135 /** Key code constant: Left Shift modifier key. */ 136 public static final int KEYCODE_SHIFT_LEFT = 59; 137 /** Key code constant: Right Shift modifier key. */ 138 public static final int KEYCODE_SHIFT_RIGHT = 60; 139 /** Key code constant: Tab key. */ 140 public static final int KEYCODE_TAB = 61; 141 /** Key code constant: Space key. */ 142 public static final int KEYCODE_SPACE = 62; 143 /** Key code constant: Symbol modifier key. 144 * Used to enter alternate symbols. */ 145 public static final int KEYCODE_SYM = 63; 146 /** Key code constant: Explorer special function key. 147 * Used to launch a browser application. */ 148 public static final int KEYCODE_EXPLORER = 64; 149 /** Key code constant: Envelope special function key. 150 * Used to launch a mail application. */ 151 public static final int KEYCODE_ENVELOPE = 65; 152 /** Key code constant: Enter key. */ 153 public static final int KEYCODE_ENTER = 66; 154 /** Key code constant: Backspace key. 155 * Deletes characters before the insertion point, unlike {@link #KEYCODE_FORWARD_DEL}. */ 156 public static final int KEYCODE_DEL = 67; 157 /** Key code constant: '`' (backtick) key. */ 158 public static final int KEYCODE_GRAVE = 68; 159 /** Key code constant: '-'. */ 160 public static final int KEYCODE_MINUS = 69; 161 /** Key code constant: '=' key. */ 162 public static final int KEYCODE_EQUALS = 70; 163 /** Key code constant: '[' key. */ 164 public static final int KEYCODE_LEFT_BRACKET = 71; 165 /** Key code constant: ']' key. */ 166 public static final int KEYCODE_RIGHT_BRACKET = 72; 167 . 168 . 169 . 170 . 171 . 172 下面还很多...
根据英语的提示，我们可以很容易地识别出，这些按键的类型，下面举个例子；
1 @Override 2 2 public boolean onKeyDown(int keyCode, KeyEvent event) { 3 3 // TODO Auto-generated method stub 4 4 5 5 if(keyCode==KeyEvent.KEYCODE_BACK){//back，返回键 6 6 Toast.makeText(this,"你按了返回键",LENGTH_LONG).show(); 7 33 } 8 35 return super.onKeyDown(keyCode, event); 9 36 }
上面是简单的一个按键时间。一般要处理很多事件的时候，用 switch - case
1 @Override 2 public boolean onKeyDown(int keyCode, KeyEvent event) { 3 // TODO Auto-generated method stub 4 if(event.getRepeatCount()==0) {//限制重复次数，防止用户过多点击 5 switch(keyCode) { 6 case KeyEvent.KEYCODE_SEARCH: 7 8 break; 9 case KeyEvent.KEYCODE_CAMERA: 10 11 break; 12 case KeyEvent.KEYCODE_DPAD_CENTER: 13 14 break; 15 16 default: 17 break; 18 } 19 } 20 return super.onKeyDown(keyCode, event); 21 }